CVE-2026-27190: 
Rust vulnerability analysis and mitigation

CVE-2026-27190 is a command injection vulnerability in Deno's node:child_process implementation, specifically caused by an incomplete shell metacharacter blocklist. It affects all Deno versions prior to 2.6.8 and was disclosed on February 19, 2026, by researcher jackhax via the GitHub Advisory Database. The vulnerability carries a CVSS v3.1 base score of 8.1 (High) per the official advisory, with high impact to confidentiality, integrity, and availability (GitHub Advisory, Deno Security Advisory).

The root cause is CWE-78 (Improper Neutralization of Special Elements used in an OS Command). When spawn or spawnSync from node:child_process is called with { shell: true } and arguments are provided, Deno's implementation previously joined the command and its arguments into a single shell string without properly escaping shell metacharacters such as newlines (\n), semicolons (;), pipes (|), backticks, and $() constructs. This allowed an attacker who can influence the arguments passed to these functions to inject additional shell commands. The fix (commit 9132ad9) introduced an escapeShellArg() function that wraps arguments in single quotes on Unix (escaping embedded single quotes) and double quotes on Windows, and also extended the metacharacter check to include \n and \r (Deno Security Advisory, Patch Commit).

Successful exploitation allows an attacker to execute arbitrary OS commands on the host system running the vulnerable Deno application, with the same privileges as the Deno process. This results in full compromise of confidentiality (unauthorized data access), integrity (unauthorized file or system modification), and availability (potential service disruption or destruction). In environments where Deno applications process user-supplied input and pass it to child_process functions with shell: true, the impact extends to lateral movement and full host takeover (GitHub Advisory, Deno Security Advisory).

A public proof-of-concept exploit is available in the official security advisory, demonstrating newline injection to achieve arbitrary command execution. The EPSS score is approximately 0.907% (76th percentile), indicating a moderate near-term exploitation probability. There is no confirmed evidence of in-the-wild exploitation at this time, and the vulnerability has not been added to the CISA Known Exploited Vulnerabilities (KEV) catalog. No specific threat actor attribution has been reported (GitHub Advisory, Deno Security Advisory).

1. Identify a vulnerable target: Locate a Deno application (version < 2.6.8) that accepts user-controlled input and passes it as arguments to spawn or spawnSync from node:child_process with the { shell: true } option enabled.
2. Craft a malicious payload: Construct an argument string containing a shell metacharacter such as a newline (\n) followed by the desired command. For example: /tmp/legitimate.ts\ntouch /tmp/rce_proof.
3. Inject the payload: Supply the malicious string as an argument to the vulnerable spawnSync or spawn call. In the PoC, this is done directly in code: spawnSync(Deno.execPath(), ['run', '--allow-all', maliciousInput], { shell: true, encoding: 'utf-8' }).
4. Trigger command execution: When Deno constructs the shell command string by joining the file and arguments without escaping, the newline character causes the shell to interpret the injected portion as a separate command, executing touch /tmp/rce_proof (or any attacker-chosen command).
5. Verify and escalate: Confirm execution by checking for the created file or other side effects. From here, an attacker can establish persistence, exfiltrate data, or pivot to other systems accessible from the host (Deno Security Advisory, GitHub Advisory).

• File System: Unexpected files created in /tmp/ or other writable directories (e.g., /tmp/rce_proof, web shells, or persistence scripts) by the Deno process; new cron jobs or startup scripts not associated with normal application behavior.
• Process: Unusual child processes spawned by the Deno runtime (e.g., bash, sh, touch, curl, wget, python, nc) that are not part of normal application operation; processes with command lines containing shell metacharacters like newlines or semicolons.
• Network: Unexpected outbound connections from the Deno process to external IPs, particularly on non-standard ports, which may indicate reverse shell or data exfiltration activity.
• Logs: Application logs showing arguments containing \n, ;, |, backticks, or $() sequences passed to child_process functions; OS-level audit logs (e.g., auditd) recording unexpected command executions by the Deno service account (Deno Security Advisory).

The vulnerability is fixed in Deno v2.6.8, released February 2, 2026. All users should upgrade immediately by running deno upgrade or downloading the latest release. No configuration-based workaround is available; the only effective remediation is upgrading to the patched version. As an interim measure where immediate patching is not feasible, restrict network access to Deno-based applications and audit code for any use of child_process functions with { shell: true } and user-controlled arguments (Deno Release v2.6.8, Deno Security Advisory).

The vulnerability was published by Deno maintainer bartlomieju and credited to reporter jackhax. It received coverage on social media platforms including Mastodon and Bluesky shortly after disclosure. Red Hat also tracked the advisory. Community reaction was generally focused on the straightforward nature of the fix and the availability of a PoC, with no major controversy or extended debate noted (Deno Security Advisory, Red Hat CVE).